Fluorescent substance, method for manufacturing the same and image display device

ABSTRACT

A fluorescent substance includes a crystal of nitride or oxy-nitride having a β-type Si 3 N 4  crystal structure having Eu +2  solid-dissolved into it and emitting a fluorescent light having a peak within a range of 500 nm to 600 nm in wavelength by being irradiated with an excitation source. The fluorescent substance further includes another crystalline or amorphous compound different from the nitride or oxy-nitride crystal and a quantity of the nitride or oxy-nitride crystal contained in the fluorescent substance is 50 wt % or more.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation application of Ser. No. 10/564,439 filed on Jan.12, 2006.

TECHNICAL FIELD

The present invention relates to a fluorescent substance having a β-typeSi₃N₄ crystal structure, a method for manufacturing the same and itsuse. More specifically, the use relates to an illuminator and an imagedisplay device which utilize the properties of the fluorescentsubstance, namely, the characteristics emitting a green fluorescentlight having an emitted light peak between 500 nm and 600 nm inwavelength by being excited by an ultraviolet light or a visible lightof 250 nm to 500 nm in wavelength or an electron beam.

BACKGROUND ART

A fluorescent substance is used in a visual fluorescence display tube(VFD), a field emission display (FED), a plasma display panel (PDP), acathode ray tube (CRT), a white light emitting diode (LED) and the like.In any of these uses, in order to make a fluorescent substance emitlight, it is necessary to provide the fluorescent substance with energyfor exciting the fluorescent substance, and a fluorescent substanceemits a visible light by being excited by an excitation source having ahigh energy of a vacuum ultraviolet light, an ultraviolet light, anelectron beam, a blue light and the like. However, as a result that afluorescent substance is exposed to such an energy source as describedabove, the fluorescent substance is liable to be reduced in luminanceand deteriorated in quality, and thus a fluorescent substance being lessin reduction of luminance is demanded. Therefore, as a fluorescentsubstance less in reduction of luminance, a sialon fluorescent substancehas been proposed instead of a conventional fluorescent substance suchas a silicate fluorescent substance, a phosphate fluorescent substance,an aluminate fluorescent substance, a sulfide fluorescent substance orthe like.

An example of such a sialon fluorescent substance is manufactured by amanufacturing process as roughly described below. It is manufactured byfirst mixing silicon nitride (Si₃Ni₄), aluminum nitride (AlN) andeuropium oxide (Eu₂O₃) together in a specified mole ratio, keeping themixture at a temperature of 1700° C. in a nitrogen atmosphere of 1 atm.(0.1 MPa) for 1 hour, and burning it by means of a hot press method (seepatent literature 1 for example). It has been reported that an α sialonhaving Eu ions activated which has been obtained by this process becomesa fluorescent substance emitting a yellow light of 550 to 600 nm bybeing excited by a blue light of 450 to 500 nm.

Further, there are known a blue light fluorescent substance having a JEMphase (LaAl(Si_(6-z)Al_(z))N_(10-z)O_(z)) as a parent crystal and havingCe activated (see patent literature 2), a blue light fluorescentsubstance having La₃Si₈N₁₁O₄ as a parent crystal and having Ce activated(see patent literature 3), and a red light fluorescent substance havingCaAlSiN₃ as a parent crystal and having Eu activated (see patentliterature 4).

However, a fluorescent substance emitting a green light in addition tofluorescent substances emitting blue and yellow lights is also demandedfor a white LED having an ultraviolet LED as an excitation source, aplasma display and the like.

Reference Literatures

Patent literature 1; Japanese Patent Laid-Open Publication No.2002-363,554Patent literature 2; Japanese Patent Application No. 2003-208,409Patent literature 3; Japanese Patent Application No. 2003-346,013Patent literature 4; Japanese Patent Application No. 2003-394,855

As another sialon fluorescent substance, a fluorescent substanceobtained by adding a rare earth element to a β-type sialon (see patentliterature 5) is known, and it has been shown that such a fluorescentsubstance having Tb, Yb or Ag activated becomes a fluorescent substanceemitting a green light of 525 nm to 545 nm. However, since an activatedelement remains in a grain boundary without being sufficientlysolid-dissolved into a crystal due to its synthesizing temperature beingas low as 1500° C., a high-luminance fluorescent substance has not beenobtained.

Reference Literature

Patent literature 5; Japanese Patent Laid-Open Publication No. Sho60-206,889

DISCLOSURE OF THE INVENTION Problem the Invention Attempts to Solve

An object of the present invention is to meet such a demand and toprovide an illuminator with a green fluorescent substance higher inluminance of green than a conventional sialon fluorescent substancehaving a rare earth element activated and more excellent in durabilitythan a conventional oxide fluorescent substance.

Means for Solving the Problem

As a result of repeating earnestly research pertaining to nitridescontaining elements such as Eu and Si, Al, O and N under suchcircumstances, the present inventors have Sound that a nitride having aparticular range of compositions, a particular solid solution state anda particular crystal phase becomes a fluorescent substance having anemitted light peak within a range of 500 nm to 600 nm in wavelength.That is to say, the inventors have found that a solid solution crystalhaving nitride or oxy-nitride with a β-type Si₃N₄ crystal structure as aparent crystal and having divalent Eu ions added as a light emittingcenter becomes a fluorescent substance emitting light having a peakwithin a range of 500 nm to 600 nm in wavelength. The inventors havefound that among others a β-type sialon synthesized at a temperature of1820° C. or higher emits a green fluorescent light being good in colorpurity and having a peak within a range of 500 nm to 550 nm inwavelength thanks to a fact that Eu is solid-dissolved into a β-typesialon crystal.

A β-type Si₃N₄ crystal structure has the symmetry of P6₃ or P6₃/m and isdefined as a structure having an ideal atom position shown in Table 1(see non-patent literature 1). As nitride or oxy-nitride having thiscrystal structure, there have known β-type Si₃N₄, β-type Ge₃N₄, β-typesialon (Si_(6-z)Al_(z)O_(z)N_(8-z), where 0≦z≦4.2) and the like. And itis known that a β-type sialon solid-dissolves no metal element into itscrystal at a synthesizing temperature of 1700° C. or lower and a metaloxide added as a sintering accelerator remains forming a glass phase ina grain boundary. In case of taking a metal element into a sialoncrystal, an α-type sialon described in patent literature 1 is used.Table 1 shows crystal structure data on the basis of the atomiccoordinates of β-type silicon nitride.

Reference Literature

Non-patent literature 1; Chong-Min Wang and four others, “Journal ofMaterials Science”, Vol. 31, 1996, pp. 5281-5298

TABLE 1 Atomic coordinates of β-type Si₃N₄ crystal x/a y/a z/c Si: 6 (h)0.7686 0.1744 0.2500 N1: 6 (h) 0.0298 0.3294 0.2628 N2: 2 (c) 0.66670.3333 0.2392 Space group: P6₃ Lattice constant a = 0.7595 nm, c =0.29023 nm R. Grun, Acta Crystal logr. B35 (1979) 800

β-type Si₃N₄ and β-type sialon have been studied a heat-resistantmaterial, and the description of solid-dissolving an optically activeelement into this crystal and using the solid-dissolved crystal as afluorescent substance is simply related to investigation of particularelements in patent literature 5.

According to patent literature 5, as a fluorescent substance having anemitted light peak within a range of 500 nm to 600 nm in wavelength,only the case where Tb, Yb or Ag is added has been reported. However, afluorescent substance having Tb added has an excitation wavelength of300 nm or less, cannot be used in a white LED and is difficult to beapplied to a display device due to an afterimage left because of itslong light emitting life. And a fluorescent substance having Yb or Agadded has a problem of being low in luminance. Until the presentinvention has been reached after that, studies for using a crystalhaving a β-type Si₃N₄ structure as a fluorescent substance have not beenperformed.

That is to say, an important discovery that nitride or oxy-nitridehaving a β-type Si₃N₄ crystal structure having a particular metalelement solid-dissolved into it can be used as a fluorescent substanceemitting a high-luminance green light by being excited by ultravioletrays, visible light, electron beam, or X rays has been performed for thefirst time by the present inventors. As a result of further repeating anearnest research on the basis of this knowledge, the present inventorshave succeeded in providing a fluorescent substance exhibiting ahigh-luminance light emitting phenomenon in a particular range ofwavelength, a method for manufacturing the same fluorescent substance,and an illuminator and an image display device having excellentcharacteristics by employing the means described in the following items(1) to (43). The means are as described in the following items (1) to(43).

(1) A fluorescent substance comprising a crystal of nitride oroxy-nitride having a β-type Si₃N₄ crystal structure having Eusolid-dissolved into it and emitting a fluorescent light having a peakwithin a range of 500 nm to 600 nm in wavelength by being irradiatedwith an excitation source.(2) A fluorescent substance according to said item (1), wherein saidcrystal having a P-type Si₃N₄ crystal structure comprises a β-typesialon (Si_(6-z)Al_(z)O_(z)N_(8-z), where 0≦z≦4.2).(3) A fluorescent substance according to said item (2), wherein thevalue of said z is “0≦z≦0.5”.(4) A fluorescent substance according to one of said items (1) to (3),wherein in case of representing Eu, A (where A is one, two or more kindsof elements selected from C, Si, Ge, Sn, B, Al, Ga and In) and X (whereX is one or two kinds of elements selected from O and N) which arecontained in said nitride or oxy-nitride crystal with a compositionformula Eu_(a)A_(b)X_(c) (where a+b+c=1), a, b and c in this formulameet the following relations (i) to (iii):

0.00001≦a≦0.1  (i)

0.38≦b≦0.46  (ii)

0.54≦c≦0.62  (iii)

(5) A fluorescent substance according to one of said items (1) to (4),wherein in case of representing said nitride or oxy-nitride crystal witha composition formula Eu_(a)Si_(b1)Al_(b2)O_(c1)N_(c2) (wherea+b₁+b₂+c₁+c₂=1), a, b₁, b₂, c₁ and c₂ in this formula meet thefollowing relations (i) to (v):

0.00001≦a≦0.1  (i)

0.28≦b₁≦0.46  (ii)

0.001≦b₂≦0.3  (iii)

0.001≦c₁≦0.3  (iv)

0.4≦c₂≦0.62  (v)

(6) A fluorescent substance according to said item (5), wherein in saidcomposition formula Eu_(a)Si_(b1)Al_(b2)O_(c1)N_(c2), the relationbetween b₁ and b₂ and the relation between c₁ and c₂ respectively meetthe following relations:

0.41≦b ₁ +b ₂≦0.44

0.56≦c ₁ +c ₂≦0.59

(7) A fluorescent substance according to one of said items (1) to (6),wherein said excitation source is an ultraviolet ray or a visible lightof 100 nm to 500 nm in wavelength.(8) A fluorescent substance according to said item (7), wherein saidexcitation source is a violet light or a blue light of 400 nm to 500 nmin wavelength.(9) A fluorescent substance according to one of said items (1) to (6),wherein said excitation source is an electron beam or an X ray.(10) A fluorescent substance according to one of said items (1) to (9),wherein said peak is within a range of 500 nm to 550 nm in wavelength.(11) A fluorescent substance according to one of said items (1) to (10),wherein x and y of the value (x, y) on the CIE chromaticity coordinatesof the color of light emitted at the time of being irradiated with saidexcitation source meet the following relations (i) and (ii):

0≦x≦0.3  (i)

0.5≦y≦0.83  (ii)

(12) A fluorescent substance according to one of said items (1) to (11),wherein said nitride or oxy-nitride crystal comprises a single crystalof 50 nm to 20 μm in average grain diameter.(13) A fluorescent substance according to one of said items (1) to (12),wherein said nitride or oxy-nitride crystal is a single crystal of 1.5to 20 in average aspect ratio.(14) A fluorescent substance according to one of said items (1) to (13),wherein the total of impurity elements Fe, Co and Ni contained in saidnitride or oxy-nitride crystal is not more than 500 ppm.(15) A fluorescent substance according to one of said items (1) to (14),wherein said nitride or oxy-nitride crystal is formed as a mixturecontaining another crystalline or amorphous compound and the quantity ofsaid nitride or oxy-nitride crystal contained in said mixture is 50 wt %(weight percents) or more.(16) A fluorescent substance according to said item (15), wherein saidanother crystalline or amorphous compound is an electrically conductiveinorganic compound.(17) A fluorescent substance according to said item (16), wherein saidelectrically conductive inorganic compound is oxide, oxy-nitride,nitride or a mixture thereof containing one, two or more kinds ofelements selected from Zn, Ga, In and Sn.(18) A fluorescent substance manufacturing method for manufacturing afluorescent substance according to one of said items (1) to (17),comprising a process of burning a raw material mixture at a temperatureof 1820° C. to 2200° C. in a nitrogen atmosphere.(19) A fluorescent substance manufacturing method according to said item(18), wherein said raw material mixture contains metal, oxide,carbonate, nitride, fluoride, chloride or oxy-nitride of Eu, and siliconnitride and aluminum nitride.(20) A fluorescent substance manufacturing method according to said item(18) or (19), said nitrogen atmosphere in said process of burning is anitrogen atmosphere within a pressure range of 0.1 MPa to 100 MPa.(21) A fluorescent substance manufacturing method according to one ofsaid items (18) to (20), further comprising a process of obtaining saidraw material mixture by filling a container with a metal compound in theform of powder or aggregate as keeping said mixture at a filling factorof 40% or less in volume density before said process of burning.(22) A fluorescent substance manufacturing method according to said item(21), wherein said container is made of boron nitride.(23) A fluorescent substance manufacturing method according to said item(21) or (22), wherein said metal compound aggregate is 500 μm or less inaverage grain diameter.(24) A fluorescent substance manufacturing method according to said item(23), further comprising a process of making said metal compoundaggregate be 500 μm or less in average grain diameter by means of spraydryer, sieving or wind classification.(25) A fluorescent substance manufacturing method according to one ofsaid items (18) to (24), wherein said burning means is not a means usinga hot press but a means using exclusively a normal pressure sinteringmethod or a gas pressure burning method.(26) A fluorescent substance manufacturing method according to one ofsaid items (18) to (25), further comprising a process ofgrain-size-adjusting the burnt fluorescent substance so as to be powderof 50 nm to 20 μm in average grain diameter by one or plural meansselected from grinding, classification and acid treatment.(27) A fluorescent substance manufacturing method according to one ofsaid items (18) to (26), further comprising a process of performing aheat treatment on a fluorescent substance after said burning process orafter said grain size adjusting process at a temperature being not lowerthan 1000° C. and being lower than a burning temperature in said processof burning.(28) A fluorescent substance manufacturing method according to one ofsaid items (18) to (27), wherein said raw material mixture contains aninorganic compound forming a liquid phase at a temperature being nothigher than the burning temperature in said process of burning.(29) A fluorescent substance manufacturing method according to said item(28), wherein said inorganic compound forming a liquid phase at atemperature being not higher than said burning temperature comprises oneor a mixture of two or more kinds of fluoride, chloride, iodide, bromideand phosphate of one, two or more kinds of elements selected from Li,Na, K, Mg, Ca, Sr and Ba.(30) A fluorescent substance manufacturing method according to said item(29), wherein said inorganic compound forming a liquid phase at atemperature being not higher than said burning temperature is calciumfluoride.(31) A fluorescent substance manufacturing method according to one ofsaid items (28) to (30), wherein said raw material mixture contains aninorganic compound forming a liquid phase at a temperature being nothigher than said burning temperature at the ratio of 0.1 to 10 in weightof said inorganic compound to 100 in weight of said raw materialmixture.(32) A fluorescent substance manufacturing method according to one ofsaid items (28) to (31), further comprising a process of cleaning saidburnt mixture with a solvent so as to reduce the quantity of saidinorganic compound forming a liquid phase at a temperature being nothigher than said burning temperature after said burning process.(33) An illuminator comprising a light emitting light source and afluorescent substance, wherein said fluorescent substance comprises afluorescent substance according to one of said items (1) to (17).(34) An illuminator according to said item (33), wherein said lightemitting light source comprises at least one of a light emitting diode(LED), a laser diode (LD), an inorganic EL device and an organic ELdevice which emit light of 330 to 500 nm in wavelength.(35) An illuminator according to said item (33) or (34), wherein saidlight emitting light source is a light emitting diode (LED) or a laserdiode (LD) which emits light of 330 to 420 nm in wavelength, and

said fluorescent substance comprises a blue fluorescent substance havinga peak of emitted light within a range of 420 nm to 500 nm inwavelength, said light being emitted by an exciting light of 330 nm to420 nm and a red fluorescent substance having a peak of emitted lightwithin a range of 600 nm to 700 nm in wavelength, said light beingemitted by an exciting light of 330 nm to 420 nm, and said illuminatoremits white light by mixing blue light, green light and red lighttogether.

(36) An illuminator according to said item (33) or (34), wherein saidlight emitting light source is a light emitting diode (LED) or a laserdiode (LD) which emits light of 420 to 500 nm in wavelength, and

said fluorescent substance comprises a red fluorescent substance havinga peak of emitted light within a range of 600 nm to 700 nm inwavelength, said light being emitted by an exciting light of 420 to 500nm, and said illuminator emits white light by mixing together blue lightof said light emitting light source, and green light and red lightemitted by said fluorescent substances.

(37) An illuminator according to one of said items (33) to (36) whereinsaid fluorescent substance comprises a yellow (or orange) fluorescentsubstance having a peak of emitted light within a range of 550 nm to 600nm in wavelength, said light being emitted by an exciting light of 300to 420 nm or 420 to 500 nm.(38) An illuminator according to said item (33) or (34), wherein saidlight emitting light source is an LED or an LD which emits light of 420to 500 nm in wavelength, and

said fluorescent substance comprises a yellow (or orange) fluorescentsubstance having a peak of emitted light within a range of 550 nm to 600nm in wavelength, said light being emitted by an exciting light of 420to 500 nm, and said illuminator emits white light by mixing togetherblue light of said light emitting light source, and green light andyellow (or orange) light emitted by said fluorescent substances.

(39) An illuminator according to said item (37) or (38), wherein saidyellow (or orange) fluorescent substance is Ca-α sialon having Eusolid-dissolved into it.(40) An illuminator according to said item (36) or (38), wherein saidred fluorescent substance comprises a fluorescent substance obtained bysolid-dissolving Eu into an inorganic material having a CaAlSiN₃ typecrystal structure.(41) An illuminator according to said item (40), wherein said inorganicmaterial having a CaAlSiN₃ type crystal structure is CaAlSiN₃.(42) An image display device comprising an excitation source and afluorescent substance, wherein said fluorescent substance comprises afluorescent substance according to one of said items (1) to (17).(43) An image display device according to said item (42), comprising atleast one of a visual fluorescent display tube (VFD), a field emissiondisplay (FED), a plasma display panel (PDP) and a cathode ray tube(CRT).

EFFECT OF THE INVENTION

Thanks to containing as its main ingredient a solid solution of acrystal phase of nitride or oxy-nitride having a β-type Si₃N₄ crystalstructure, a fluorescent substance of the present invention has a higherintensity of light emitted within a range of 500 nm to 600 nm inwavelength than a conventional sialon or oxy-nitride fluorescentsubstance and is more excellent as a green fluorescent substance. Thisfluorescent substance provides a nitride to be a useful fluorescentsubstance to be preferably used in VFD, FED, PDP, CRT, white LED and thelike without being reduced in luminance even in case of being exposed toan excitation source.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an X-ray diffraction chart of an inorganic compound ofembodiment 1.

FIG. 2 shows a scanning electron microscope (SEM) image of the inorganiccompound of embodiment 1.

FIG. 3-1 shows a transmission electron microscope (TEM) image of theinorganic compound of embodiment 1.

FIG. 3-2 shows a transmission electron microscope (TEM) image of theinorganic compound of embodiment 1 in a high resolution.

FIG. 3-3 shows observed spectra of Eu in a grain by an electron beamenergy loss analyzer (EELS) attached to TEM.

FIG. 4-1 shows emitted light spectrum showing a light emittingcharacteristic of the inorganic compound of embodiment 1.

FIG. 4-2 shows an image observed by a cathode luminescence detector (CL)of the inorganic coin-pound of embodiment 1.

FIG. 5 shows an excitation spectrum and an emitted light spectrum ofembodiment 1 obtained by fluorometry.

FIG. 6 shows an emitted light spectrum of comparative example 2.

FIG. 7 shows emitted light spectra of comparative examples 3 to 5.

FIG. 8 shows an emitted light spectrum of comparative example 6.

FIG. 9 shows an emitted light spectrum of embodiment 31 before an acidtreatment.

FIG. 10 shows an emitted light spectrum of comparative example 31 afteran acid treatment.

FIG. 11 is a schematic diagram of an illuminator (LED illuminator)according to the present invention.

FIG. 12 is a schematic diagram of an image display device (plasmadisplay panel) according to the present invention.

DESCRIPTION OF THE SYMBOLS

1. A mixture of a green fluorescent substance (embodiment 1) of thepresent invention, a red fluorescent substance and a blue fluorescentsubstance, or a mixture of a green fluorescent substance (embodiment 1)of the present invention and a red fluorescent substance, or a mixtureof a green fluorescent substance (embodiment 1) of the present inventionand a yellow fluorescent substance.2: LED chip, 3, 4: Conductive terminals, 5: Wire bond, 6: Resin layer,7: Container, 8: Red fluorescent substance, 9: Green fluorescentsubstance, 10: Blue fluorescent substance, 11, 12, 13: Ultraviolet rayemitting cells, 14, 15, 16, 17: Electrodes, 18, 19: Dielectric layer 20:Protective layer, 21, 22: Glass substrates

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention are described in detail in thefollowing.

A fluorescent substance of the present invention contains as its mainingredient a solid solution of a crystal phase of nitride or oxy-nitridehaving a β-type Si₃N₄ crystal structure (hereinafter, referred to as aβ-type Si₃N₄ group crystal). A β-type Si₃N₄ group crystal can beidentified by an X-ray diffraction or a neutron flux diffraction, and inaddition to a substance exhibiting the same diffraction as a pure β-typeSi₃N₄, a substance whose lattice constant is varied due to replacementof a component element of it with another element is also included inthe β-type Si₃N₄ group crystal. Further, depending on the form of solidsolution, a point defect, a plane defect or a stacking fault isintroduced in a crystal and a solid-dissolved element may beconcentrated in a defective part in a grain, but a substance in whichthe form of a chart obtained by an X-ray diffraction is not varied is aβ-type Si₃N₄ group crystal. And a substance having a β-type Si₃N₄crystal structure as its basic structure also in case of forming apolytype having a long-periodic structure due to a periodicity offormation of defects is a β-type Si₃N₄ group crystal.

Hereupon, a pure β-type Si₃N₄ crystal structure belongs to a hexagonalsystem having the symmetry of P6₃ or P6₃/m, and is a crystal defined asa structure having an ideal atom position of Table 1 (see non-patentliterature 1). In an actual crystal, the position of each atom is variedby a degree of ±0.05 from its ideal position according to the kind ofeach atom occupying its position.

Although a=0.7595 nm and c=0.29023 nm for its lattice constant, thelattice constant is varied by a fact that Si being a component of it isreplaced with another element such as Al or the like, or N is replacedwith another element such as 0 or the like, or a metal element such asEu or the like is solid-dissolved, but its crystal structure, a siteoccupied by the atom and the atom position given by its coordinates arenot greatly varied. Therefore, if a lattice constant and a face index ofa pure β-type Si₃N₄ are given, the position of a diffraction peak (2θ)by an X-ray diffraction is uniquely determined. And when a latticeconstant calculated from the result of an X-ray diffraction measured fora new substance and data of a peak position of diffraction (2θ)calculated using a face index of Table 4 coincide with each other, it ispossible to identify that the said crystal structures are the same aseach other.

As a nitride or oxy-nitride crystal having a β-type Si₃N₄ crystalstructure, there can be mentioned β-type Si₃N₄, β-type Ge₃N₄, β-typeC₃N₄ and a solid solution thereof, without specifying a particularsubstance having the same crystal structure as a nitride or oxy-nitridecrystal having a β-type Si₃N₄ crystal structure. As a solid solution, inthe position of Si of a β-type Si₃N₄ crystal structure, Si can bereplaced with an element such as C, Si, Ge, Sn, B, Al, Ga or In, and inthe position of N, N can be replaced with an element such as O or N. Thereplacement of these elements includes a simultaneous replacement of notonly one kind but also two or more kinds of elements. It is β-type Si₃N₄and β-type sialon (Si_(6-z)Al_(z)O_(z)N_(8-z), where 0<z<4.2) thatprovides a particularly high luminance among these crystals.

In the present invention, it is desirable that a crystal phase ofnitride or oxy-nitride having a β-type Si₃N₄ crystal structure as itsmain ingredient is contained as much as possible at a high purity and isformed out of a single phase if possible, but can be composed of amixture with another crystal phase or amorphous phase within a range inwhich its characteristics do not degrade. In this case, in order toobtain a high luminance, it is desired that the amount of containedcrystal phase of nitride or oxy-nitride having a β-type Si₃N₄ crystalstructure is 50 wt % or more. The range of a main ingredient in thepresent invention is at least 50 wt % or more in content amount of acrystal phase of nitride or oxy-nitride having a β-type Si₃N₄ crystalstructure.

Bivalent Eu ions act as the center of light emission and exhibit thefluorescent characteristics by using a crystal of nitride or oxy-nitridehaving a β-type Si₃N₄ crystal structure as a parent crystal andsolid-dissolving a metal element Eu into the parent crystal. Further, aβ-type sialon crystal containing Eu, namely, a crystal containing Al andEu in it is excellent in light emitting characteristic of green light inparticular.

A fluorescent substance of the present invention emits a fluorescentlight having a peak within a range of 500 nm to 600 nm in wavelength bybeing irradiated with an excitation source. An emitted light spectrumhaving a peak within this range emits a green light. Among others, thecolor of emitted light in a spectrum of a sharp shape having a peakwithin a range of 500 nm to 550 nm in wavelength is a green color whichtakes the values of “0≦x≦0.3 and 0.5≦y≦0.83” in terms of the value (x,y) on the CIE chromaticity coordinates and is good in color purity.

As an excitation source of the fluorescent substance, the use of lightof 100 nm to 500 nm in wavelength (vacuum ultraviolet ray, deepultraviolet ray, ultraviolet ray, near ultraviolet ray, violet to bluevisible light), an electron beam, X rays and the like emits ahigh-luminance fluorescent light.

In the present invention, a crystal of nitride or oxy-nitride having aβ-type Si₃N₄ crystal structure is not particularly specified in kind ofits composition, but a fluorescent substance being high in content ratioof a crystal of nitride or oxy-nitride having a β-type Si₃N₄ crystalstructure and being high in luminance can be obtained by the followingcomposition.

As composition by which a fluorescent substance being high in contentratio of a crystal of nitride or oxy-nitride having a β-type Si₃N₄crystal structure and being high in luminance can be obtained, thecomposition within the following range is preferable. The compositioncontains Eu, A (where A is an element C, Si, Ge, Sn, B, Al, Ga or In)and X (where X is one or two kinds of elements selected from O and N),and is represented by a composition formula Eu_(a)A_(b)X_(c) (wherea+b+c=1), where the values of a, b and c are selected from the valuesmeeting all of the following conditions (i) to (iii):

0.00001≦a≦0.1  (i)

0.38≦b≦0.46  (ii)

0.54≦c≦0.62  (iii)

“a” represents the amount of addition of element Eu to be the lightemitting center, and is preferably not less than 0.00001 and not morethan 0.1 at atom ratio. Since the number of Eu atoms to be the lightemitting center is small when value a is less than 0.00001, theluminance of emitted light is lowered. When value a is more than 0.1,the luminance is lowered due to the density extinction caused byinterference between Eu ions.

“b” is the amount of metal element forming a parent crystal and ispreferably not less than 0.38 and not more than 0.46 at atom ratio.Preferably b=0.429. When value b is out of this range, the bond in acrystal becomes unstable and the ratio of formation of crystal phasesother than a β-type Si₃N₄ crystal structure is increased and thereby theintensity of emitted green light is lowered.

“c” is the amount of non-metal elements forming the parent crystal andis preferably not less than 0.54 and not more than 0.62 at atom ratio.Preferably c=0.571. When value c is out of this range, the bond in acrystal becomes unstable and the ratio of formation of crystal phasesother than a β-type Si₃N₄ crystal structure is increased and thereby theintensity of emitted green light is lowered.

In case of taking a β-type sialon as a parent crystal and using Eu as alight emitting center, a fluorescent substance being particularly highin luminance can be obtained by the following composition. Thecomposition is represented by Eu_(a)Si_(b1)Al_(b2)O_(c1)N_(c2) (wherea+b₁+b₂+c₁+c₂=1), and a, b₁, b₂, c₁ and c₂ are selected from the valuesmeeting all of the following conditions (i) to (v):

0.00001≦a≦0.1  (i)

0.28≦b₁≦0.46  (ii)

0.001≦b₂≦0.3  (iii)

0.001≦c₁≦0.3  (iv)

0.44≦c₂≦0.62  (v)

“b₁” is the amount of Si, and is preferably not less than 0.28 and notmore than 0.46 at atom ratio. “b₂” is the amount of Al, and ispreferably not less than 0.001 and not more than 0.3 at atom ratio. Andthe total of values b₁ and b₂ is preferably not less than 0.41 and notmore than 0.44, and more preferably is 0.429. When values b₁ and b₂ areout of this range, the ratio of formation of crystal phases other than aβ-type sialon is increased and thereby the intensity of emitted greenlight is lowered.

“c₁” is the amount of oxygen, and is preferably not less than 0.001 andnot more than 0.3 at atom ratio. “c₂” is the amount of nitrogen, and ispreferably not less than 0.54 and not more than 0.62 at atom ratio. Andthe total of values c₁ and c₂ is preferably not less than 0.56 and notmore than 0.59. More preferably c=0.571. When values c₁ and c₂ are outof this range, the ratio of formation of crystal phases other thanβ-type sialon is increased and thereby the intensity of emitted greenlight is lowered.

And these compositions may contain other elements as impurities in arange in which the characteristics are not deteriorated. Impuritiesdeteriorating the light emitting characteristics are Fe, Co, Ni and thelike, and when the total of these three elements exceeds 500 ppm, theluminance of emitted light is lowered.

In the present invention, it is desired that a crystal phase is formedout of a single phase of a crystal phase of nitride or oxy-nitridehaving a β-type Si₃N₄ crystal structure, but it can be also formed outof a mixture with another crystal phase or amorphous phase within arange in which the characteristics are not deteriorated. In this case,in order to obtain a high luminance, it is desired that the amount ofcontained crystal phase of nitride or oxy-nitride having a β-type Si₃N₄crystal structure is 50 wt % or more.

The range of a main ingredient in the present invention is at least 50wt % or more in content amount of a crystal phase of nitride oroxy-nitride having a β-type Si₃N₄ crystal structure. The ratio ofcontent amount can be obtained by performing an X-ray diffractionmeasurement and comparing with each other the intensities of therespective most intense peaks of a crystal phase of nitride oroxy-nitride having a β-type Si₃N₄ crystal structure and crystal phasesother than it.

A fluorescent substance formed out of a mixture with another crystalphase or amorphous phase can be mixed with an electrically conductiveinorganic substance. In case of exciting a fluorescent substance of thepresent invention with an electron beam in VFD, PDP and the like, it ispreferable that the fluorescent substance has some conductivity in orderto discharge electrons to the outside without making the electrons stayon the fluorescent substance.

As electrically conductive materials there can be mentioned oxide,oxy-nitride, nitride or a mixture thereof containing one, two or morekinds of elements selected from Zn, Ga, In and Sn. Among others, indiumoxide and indium-tin oxide (ITO) are more preferable since they are lessin reduction of intensity of fluorescence and higher in conductivity.

Although the form of a fluorescent substance of the present invention isnot specified in particular, in case that it is used as powder, it ispreferably a single crystal of 50 nm to 20 μm in average grain diameterin order to obtain a high luminance. Furthermore, a single crystal of1.5 to 20 in average aspect ratio (the value of the length of the majoraxis of a grain divided by the length of the minor axis) provides afurther higher luminance. An average grain diameter larger than 20 μm isnot preferable due to making the fluorescent substance poor indispersiveness in being used in an illuminator or an image displaydevice.

Fluorescent substance powder being smaller in average grain diameterthan 50 nm becomes poor in operability due to aggregation of powder. Asingle crystal grain of 1.5 or more in average aspect ratio (the valueof the length of the major axis of a grain divided by the length of theminor axis) provides a particularly high-luminance light. Thisincorporates a relatively more amount of metal elements such as Eu andthe like into a crystal having a β-type silicon nitride structure whenthe crystal grows, and provides a high-luminance light due to a smallamount of defects hindering the fluorescence and due to a relativelyhigh transparency. However, an aspect ratio higher than 20 is notpreferable from, the viewpoint of environment due to making needlecrystals. In such a case it is enough to grind the needle crystals by amanufacturing method of the present invention.

A method for manufacturing a fluorescent substance of the presentinvention is not specified in particular, but the following method canbe mentioned as an example.

A raw material mixture which is a mixture of metal compounds and canform composition Eu_(a)Si_(b)Al_(c)O_(d)N_(e) by burning is burned in anitrogen atmosphere. Since the optimal burning temperature is differentdepending on the composition, it can be unconditionally prescribed, butgenerally a green fluorescent substance can be stably obtained within atemperature range of 1820° C. to 2200° C. At a burning temperature beinglower than 1820° C., since element Eu to be a light emitting centerremains in a grain boundary containing much oxygen without beingsolid-dissolved into a nitride or oxy-nitride crystal having a β-typeSi₃N₄ crystal structure, the result provides a light emission havingoxide glass as a host to emit a low-wavelength light such as blue or thelike without providing a green fluorescent light. According to patentliterature 5, the burning temperature is 1550° C. and Eu remains in agrain boundary. That is to say, in patent literature 5, even in case ofusing the same Eu as an active element, the wavelength of emitted lightis blue between 410 and 440 nm and is essentially different from thewavelength between 500 and 550 nm of light emitted by a fluorescentsubstance of the present invention. And a burning temperature being notlower than 2200° C. requires a special apparatus and therefore is notpreferable industrially.

A mixture of metal compounds may be preferably a mixture formed out ofan Eu containing metal compound selected from metal, oxide, carbonate,nitride or oxy-nitride of Eu, and silicon nitride and aluminum nitride.These have an advantage of being produced as industrial raw materialsand easy to obtain in addition to being excellent in reactivity andbeing able to provide a high-purity compound.

In order to improve the reactivity during a burning process, it ispossible to add an inorganic compound forming a liquid phase at atemperature being not higher than the burning temperature to a mixtureof metal compounds according to need. As the inorganic compound, acompound forming a stable liquid phase at a reaction temperature ispreferable, and fluoride, chloride, iodide, bromide or phosphate of suchan element as Li, Na, K, Mg, Ca, Sr or Ba is suitable.

Further, these inorganic compounds each may be added singly and may beadded as a mixture of two or more kinds of the compounds. Among others,calcium fluoride is suitable due to being high in ability to improve thereactivity in synthesis. Although the amount of addition of inorganiccompounds is not prescribed in particular, the ratio of 0.1 to 10 inweight of inorganic compound to 100 in weight of a metal compound beinga starting raw material provides a particularly large effect.

Being smaller than 0.1 in weight is less in improvement of thereactivity and exceeding 10 in weight lowers the luminance of afluorescent substance. To add and burn these inorganic compoundsimproves the reactivity, grows a single crystal being large in graindiameter by promoting growth of grains in a comparatively short time,and improves the luminance of a fluorescent substance. Further, reducingthe amount of inorganic compounds contained in a reactant obtained byburning by cleaning the burnt mixture with a solvent to solve theinorganic compounds after burning improves the luminance of thefluorescent substance. As such a solvent, there can be mentioned water,ethanol, sulfuric acid, hydrofluoric acid and a mixture of sulfuric acidand hydrofluoric acid.

The nitrogen atmosphere is preferably a gas atmosphere within a pressurerange of 0.1 MPa to 100 MPa. More preferably it is not lower than 0.5MPa and not higher than 10 MPa. In case of using a silicon nitride as araw material, when heating to a temperature of 1820° C. or higher, anitrogen atmosphere being lower than 0.1 MPa is not preferable since theraw material is thermally decomposed. When it is higher than 0.5 MPa,the raw material is hardly decomposed. A pressure of 10 MPa is enough,but a pressure of 100 MPa or higher requires a special apparatus and isnot suitable for industrial production.

According to a method of filling a container with a metal compound inthe form of powder or aggregate as keeping the metal compound at afilling factor of 40% or less in volume density and then burning themetal compound, a particularly high luminance can be obtained. In caseof using fine powder of several microns in grain diameter as a startingraw material, a mixture of metal compounds which have passed a mixingprocess makes a form in which fine powder of several microns in graindiameter aggregates into the size of several hundred microns to severalmillimeters (referred to as a powder aggregate). The present inventionburns a powder aggregate in a state of keeping it at a filling factor of40% or less in volume density.

That is to say, while a conventional sialon manufacturing methodperforms a burning process at a high filling factor of powder after ahot press or metal-mold molding, the present invention fills a containerwith a mixture of powder aggregate being uniform in grain size as it isat a filling factor of 40% or less in volume density without molding thepowder aggregate by means of metal molds or the like in advance.According to need, it can control the said powder aggregate in grainsize by making grains be 500 μm or less in average grain diameter bymeans of sieving or wind classification. And the powder aggregate may bedirectly made into grains of 500 μm or less by means of a spray dryerand the like. And a container made of boron nitride has an advantage ofbeing less reactive with a fluorescent substance.

The reason why a burning process is performed as keeping a fillingfactor of 40% or less in volume density is that when a burning processis performed in a state where a free space exists around raw materialpowder, crystals come into less contact with one another due to a factthat reaction products grow into crystal in the free space, and acrystal being less in surface defect can be synthesized. Thanks to this,a high-luminance fluorescent substance can be obtained. A volume densityof 40% or more generates densification partially during a burningprocess, results in forming a dense sinter to hinder the growth ofcrystal and lowers the luminance of a fluorescent substance. And finepowder cannot be obtained. And the size of powder aggregate isparticularly preferable to be 500 μm or less due to being excellent ingrindability after burning.

Next, powder aggregate being 40% or less in filling factor is burnedunder the above-mentioned condition. Since a burning temperature is highand a burning atmosphere is nitrogen, a furnace to be used in a burningprocess is preferably an electric furnace of a metal resistance heatingtype or a graphite resistance heating type using carbon as a materialfor a high-temperature portion of the furnace. A burning method ispreferably a sintering method such as a normal pressure sinteringmethod, a gas pressure sintering method and the like which apply nomechanical pressure from the outside due to burning as keeping thevolume density high.

In case that a powder aggregate obtained by burning is firmly hardened,the powder aggregate is ground by such a grinder usually used in afactory as a ball mill, a jet mill or the like, for example. Amongothers, ball-mill grinding makes it easy to control grain size. A balland a pot used at this time are preferably made of a silicon nitridesinter or a sialon sinter. More preferably, they are made of ceramicsinter having the same composition as a fluorescent substance to be aproduct. A grinding process is performed until the average grain sizebecomes 20 μm or less. More preferably the average grain size is notless than 20 nm and not more than 5 μm. When the average grain sizeexceeds 20 μm, the flowability and the dispersibility of powder in resinis made bad, and when forming a light emitting apparatus in combinationwith a light emitting device, the intensity of luminance is made unevendepending on parts. The average grain size of 20 nm or less makes theoperability of handling the powder poor. In case of being unable toobtain a desired grain size by only grinding, it is possible to combinegrinding with classification. As a method of classification, a sievingmethod, a wind classification method, an in-liquid precipitation methodor the like can be used.

An acid treatment may be performed as one method of grindingclassification. In many cases, a powder aggregate obtained by burning isin a state where single crystals of nitride or oxy-nitride having aβ-type Si₃N₄ crystal structure are firmly hardened in a grain boundaryphase having a minute amount of glass phase as its main component. Inthis case, when the powder aggregate is immersed in an acid having aspecific composition, a grain boundary phase having a glass phase as itsmain component is selectively dissolved and single crystals areseparated. Due to this, each grain is obtained not as aggregate ofsingle crystals but as a grain composed of a single crystal of nitrideor oxy-nitride having a β-type Si₃N₄ crystal structure. Such a grainprovides a fluorescent substance being particularly high in luminancedue to being composed of a single crystal having less surface defects.

As acid being effective for this treatment, there can be mentionedhydrofluoric acid, sulfuric acid, hydrochloric acid, and a mixture ofhydrofluoric acid and sulfuric acid. Among others, a mixture ofhydrofluoric acid and sulfuric acid is high in effect of removing aglass phase.

Although fine powder of a fluorescent substance is obtained by the aboveprocess, a heat treatment is effective in order to further improve theluminance. In this case, powder after burning or powder after beingadjusted in grain size by grinding or classification can be heat-treatedat a temperature being not lower than 1000° C. and being not higher thana burning temperature. A temperature being lower than 1000° C. reducesan effect of removing surface defects. A temperature being not lowerthan the burning temperature is not preferable due to a fact that groundpowder is hardened again. An atmosphere suitable for heat treatmentvaries according to the composition of a fluorescent substance, but amixed atmosphere of one kind or two or more kinds selected fromnitrogen, airs ammonia and hydrogen can be used, and particularly anitrogen atmosphere is preferable due to being excellent in effect ofremoving defects.

A nitride of the present invention obtained as described above ischaracterized in having a broader excitation range from ultraviolet raysto visible light in comparison with a conventional oxide fluorescentsubstance or an existing sialon fluorescent substance and in emitting agreen light having a peak within a range of 500 nm to 600 nm, and issuitable for an illuminator and an image display device. In addition tothis, it is excellent in thermal resistance due to being notdeteriorated even by being exposed to a high temperature and is alsoexcellent in stability for a long period under an oxidizing atmosphereand a moisture environment.

An illuminator of the present invention is composed of at least a lightemitting light source and a fluorescent substance of the presentinvention. As an illuminator, there are an LED illuminator, afluorescent lamp, an EL illuminator and the like. An LED illuminator canbe manufactured using a fluorescent substance of the present inventionby means of a publicly known method as described in Japanese PatentLaid-Open Publication No. Hei 5-152,609, Japanese Patent Laid-OpenPublication No. Hei 7-99,345, Japanese Patent Publication No. 2,927,279and the like. In this case, a light emitting light source is preferablya light source emitting light of 330 to 500 nm in wavelength, and amongothers, an ultraviolet (or violet) LED light emitting device or LD lightemitting device of 330 to 420 nm and a blue LED or LD light emittingdevice of 420 to 500 nm are preferable.

Some of these light emitting devices is made of a nitride semiconductorsuch as GaN, InGaN or the like, and can become a light emitting lightsource emitting light of specified wavelength by adjusting thecomposition of it.

It is possible to form an illuminator emitting light having a desiredcolor by using singly a fluorescent substance of the present inventionin an illuminator and additionally to this method, using jointly afluorescent substance having another light emitting characteristic. Asan example of this, there is a combination of an ultraviolet LED or LDlight emitting device of 330 to 420 nm, a blue fluorescent substancehaving a light emitting peak between 420 nm and 500 nm in wavelength bybeing excited by this wavelength, a red fluorescent substance having anemitted light peak between 600 nm and 700 nm in wavelength and a greenfluorescent substance of the present invention. There can be mentionedBaMgAl₁₀O₁₇:Eu as such a blue fluorescent substance and CaSiAlN₃:Eudescribed in Japanese Patent Application No. 2003-394,855 as a redfluorescent substance. In this composition, when fluorescent substancesare irradiated with an ultraviolet ray emitted by an LED or LD, lightsof three colors of red, green and blue are emitted and a whiteilluminator is made by mixture of these colors.

As another technique, there is a combination of a blue LED or LD lightemitting device of 420 to 500 nm, a red fluorescent substance having alight emitting peak between 600 nm and 700 nm by being excited by thiswavelength and a fluorescent substance of the present invention. Therecan be mentioned CaSiAlN₃:Eu described in Japanese Patent ApplicationNo. 2003-394,855 as such a red fluorescent substance. In thiscomposition, when a fluorescent substance is irradiated with a bluelight emitted by an LED or LD, lights of two colors of red and green areemitted and a white or reddish electric-lamp colored illuminator is madeby mixture of these and a blue light of the LED or LD itself.

As another technique, there is a combination of a blue LED or LD of 420to 500 nm, a yellow or orange fluorescent substance having a lightemitting peak between 550 nm and 600 nm by being excited by thiswavelength and a fluorescent substance of the present invention. Therecan be mentioned (Y, Gd)₂(Al, Ca)₅O₁₂:Ce described in Japanese PatentLaid-Open Publication No. Hei 9-218,149 or α-sialon:Eu described inJapanese Patent Laid-Open Publication No. 2002-363,554 as such a yellowor orange fluorescent substance. Among others, Ca-α-sialon having Eusolid-dissolved into it is preferable due to its high luminance ofemitted light. In this composition, when a fluorescent substance isirradiated with a blue light emitted by an LED or LD, lights of twocolors of yellow or orange and green are emitted and a white illuminatoris made by mixture of these and a blue light of the LED or LD itself.And it is possible to adjust the color of light of an illuminator intovarious colors such as bluish white, white and reddish electric-lampcolor by changing the ratio of two kinds of fluorescent substances to becombined.

An image display device of the present invention is composed of at leastan excitation source and a fluorescent substance of the presentinvention, and includes a visual fluorescent display tube (VFD), a fieldemission display device (FED), a plasma display panel (PDP), a cathoderay tube (CRT) and the like. It has been confirmed that a fluorescentsubstance of the present invention emits light by excitation of a vacuumultraviolet ray of 100 to 190 nm, an ultraviolet ray of 190 to 380 nm,an electron beam and the like, and an image display device as describedabove can be composed by a combination of these excitation sources and afluorescent substance of the present invention.

Next, the present invention is described in more detail on the basis onembodiments shown in the following, but these are disclosed only as anaid to easily understand the present invention and the present inventionis not limited to these embodiments.

Embodiment 1

As raw material powder, there were used silicon nitride powder being 0.5μm in average grain size and containing oxygen of 0.93 wt % and α-typeof 92%, aluminum nitride powder being 3.3 m²/g in specific surface areaand containing oxygen of 0.79% and europium oxide powder of 99.9% inpurity.

In order to obtain a compound shown by a composition formulaEu_(0.00296)Si_(0.41395)Al_(0.01334)O_(0.00444)N_(0.56528) (Designedcomposition is shown in Table 2, and mixture composition and burningtemperature of the raw material powder are shown in Table 3), thesilicon nitride powder, the aluminum nitride powder and the europiumoxide powder were weighed so that they were respectively 94.7 wt %, 2.68wt % and 2.556 wt %, and were mixed for 2 hours by a wet ball mill usinga pot made of silicon nitride sinter, balls made of silicon nitridesinter and n-hexane.

Dried mixture powder was obtained by removing n-hexane by means of arotary evaporator. A powder aggregate being excellent in flowability wasobtained by grinding the obtained mixture by means of an agate mortarand pestle and then passing the ground mixture through a sieve of 500μm. When this powder aggregate was put into a crucible made of boronnitride of 20 mm in diameter and 20 mm in height by natural falling, thevolume density of 30 vol % was obtained. The volume density wascalculated from the weight of the powder aggregate put into and thecapacity of the crucible.

Next, the crucible was set on an electric furnace of a graphiteresistance heating type. A burning process first made a burningatmosphere vacuum using a diffusion pump, heated the crucible at heatingrate of 500° C./hour from room temperature to 800° C., introducednitrogen of 99.999 vol % in purity at 800° C. to make 1 MPa in pressure,heated the crucible to 1900° C. at a heating rate of 500° C./hour, andkept it at 1900° C. for 8 hours.

The synthesized sample was ground by means of the agate mortar and apowder X-ray diffraction measurement (XRD) using Kα-rays of Cu wasperformed. A chart obtained as a result showed a pattern shown in FIG.1, from which it was found by a composition analysis that a β-typesialon having a β-type silicon nitride structure and containing Al and Owas generated. This burnt object obtained was roughly ground and thenwas ground by means of a mortar and pestle made of silicon nitride. Whenthe grain size distribution was measured, the average grain size of 4 μmwas obtained.

The composition analysis of this powder was performed by the followingmethod. First, this method put a sample of 50 mg into a platinumcrucible, added sodium carbonate of 0.5 g and boric acid of 0.2 g to thesample, heated and melted the sample and then dissolved the sample intohydrochloric acid of 2 ml to make a solution for measurement having aconstant volume of 100 ml. The method quantified the quantities of Si,Al, Eu and Ca in the powder sample by performing an ICP light emissionspectroscopic analysis on this liquid sample. And the method put thesample of 20 mg into a tin capsule and quantified oxygen and nitrogen inthe powder sample by measuring this capsule put into a nickel basket bymeans of an oxygen and nitrogen analyzer of Model TC-436 made by LECO,Inc.

Further, in order to quantify the amount of impurities being a minuteamount of components in the powder, the method quantified the amounts ofimpurities B, Fe, Ca, Mg, Al and Cr by mixing and cramming the sample of50 mg and graphite powder of 50 mg into a graphite electrode and using aCID-DCA light emission spectroscopic analysis apparatus made by JapanJarel-Ash Co. The measurement by the ICP light emission spectroscopicanalysis and the oxygen and nitrogen analyzer provided the result thatEu of 2.16±0.02 wt %, Si of 55.6±0.1 wt %, Al of 1.64±0.1 wt %, N of38.0±0.1 wt %, and O of 2.1±0.1 wt %.

The composition (represented by the number of atoms) of the synthesizedinorganic compound calculated from the result of analysis of all theelements is Eu_(0.00290)Si_(0.40427)Al_(0.01210)O_(0.02679)N_(0.55391).This is particularly high in oxygen content in comparison with thedesigned composition(Eu_(0.00296)Si_(0.41395)Al_(0.01334)O_(0.00444)N_(0.56528)) shown inTable 2. This is caused by impurity oxygen contained in the siliconnitride and aluminum nitride used as raw materials. A sialon compositionof the present invention is ideally a composition ofSi_(6-z)Al_(z)O_(z)N_(8-z) (where 0<z<4.2), but a composition in whichpart of N component in this composition is replaced with 0 falls alsowithin the scope of the present invention, and in such a case also, agreen fluorescent substance being high in luminance can be obtained.

And as impurity elements detected by the CID-DCA light emissionspectroscopic analysis, there were Y of 0.009 wt %, B of 0.001 wt %, Feof 0.003 wt %, Ca of 0.001 wt % or less, Mg of 0.001 wt % or less, andCr of 0.001 wt % or less.

The form of this powder was observed by means of a scanning electronmicroscope (SEM). As shown in FIG. 2, it was confirmed that the powderwas composed of needle crystals each being about 100 to 500 nm in minoraxis and about 4 μm in major axis. A crystal of such a form shows thatit was crystal-grown through a gas phase or a liquid phase in a freespace, and is essentially different from the synthesis at a lowtemperature of 1800° C. or lower.

The form of this powder was observed by means of a transmission electronmicroscope (TEM) (FIGS. 3-1 and 3-2). As shown in FIG. 3-1, a grain is asingle crystal having no grain boundary and is characterized in havinglittle defects in the grain. And according to a high-resolutionobservation (FIG. 3-2), it has been confirmed that there is an amorphousphase of 0.7 nm on the surface of a single crystal grain but there arenot another amorphous and crystal phase.

This amorphous phase is a silicon oxide made by oxidation of the surfaceof a grain. In order to examine the existence of Eu in this grain,spectra of Eu were measured using an electron beam energy loss analyzer(EELS) attached to the TEM (FIG. 3-3). It has been confirmed that thespectra showing the states of Eu electrons on the surface (chart (a) inFIG. 3-3) and in the middle (chart (b) in FIG. 3-3) of a grain arealmost the same as each other and these are the same as the spectrum ofeuropium oxide (Eu₂O₃; chart (c) in FIG. 3-3) being a reference sample.That is to say, it has been confirmed that E exists in a grain and isnot unevenly distributed on an amorphous surface phase.

The uniformity of this powder was observed by an SEM provided with acathode luminescence (CL) detector and a cathode luminescence image wasevaluated. This apparatus irradiates a sample with an electron beam,detects a visible light generated thereby, acquires a photographic imagebeing two-dimensional information and thereby clarifies at what placeand of what wavelength light is emitted. By observing the spectrum of anemitted light of FIG. 4-1, it has been confirmed that this fluorescentsubstance emits a green light of 530 nm in wavelength through beingexcited by an electron beam. And according to a CL image having severalten grains observed (FIG. 4-2), it has been confirmed that a spot wherea particular part emits light does not exist and the inside of a grainemits uniformly green light. And it has been confirmed that no grainemits a particularly intense light and all of the several ten grainsuniformly emit green light.

The CL image shows that a part whitely observed is a part emitting lightof 530 nm, and the whiter the black and white gradation display is themore intense a green light emitted is.

Integrating the results of observation of the XRD charts, SEM images,TEM images, EESL spectra and CL images shown above, the following factshave been confirmed for this powder:

(1) The powder is an inorganic substance having a β-type sialon of aβ-type Si₃N₄ structure as its parent structure and having Eusolid-dissolved into it;(2) Its composition isEu_(0.00290)Si_(0.40427)Al_(0.01210)O_(0.02679)N_(0.55391);(3) Eu is uniformly distributed in a β-type sialon crystal;(4) The powder is a single phase substance not having other phases suchas a second phase, a grain boundary phase and the like formed;(5) Each grain is one single crystal; and(6) Each grain emits light uniformly.

A fluorescent having such characteristics has not been reported up tonow and has been found for the first time by the present inventors.

It has been confirmed that a green light is emitted as a result ofirradiating this powder with light of 365 nm in wavelength emitted by alamp. As a result of measuring the spectrum of emitted light of thispowder and the spectrum of excitation (FIG. 5) by means of a fluorescentspectrophotometer, it has found that this powder is a fluorescentsubstance having an excitation spectrum peak at 303 nm and a green lightpeak at 535 nm in the spectrum of light emitted by excitation of 303 nm.

The intensity of emitted light at the peak was 3948 counts. The countvalue has an arbitrary unit as its unit due to varying according tomeasurement apparatus or measurement conditions. That is to say, countvalues can be compared with one another only in the embodiments andcomparative examples measured under the same conditions. The CIEchromaticity of light emitted by excitation of 303 nm was a green colorof “x=0.32, y=0.64”.

Embodiments 2 to 24 were performed on the basis of a similar method andprocedure to embodiment 1. Their designed compositions and the mixturecompositions of raw material powder are shown collectively in Tables 2and 3.

TABLE 2 Designed Composition Designed composition (atom ratio) Eu Si AlO N Embodiment 1 0.002966 0.413952 0.013348 0.004449 0.565284 2 0.0014270.421541 0.006419 0.002140 0.568474 3 0.004415 0.419426 0.0051510.006623 0.564386 4 0.001478 0.421286 0.006652 0.002217 0.568367 50.000444 0.421941 0.007180 0.000666 0.569768 6 0.009105 0.4097120.010622 0.013657 0.556904 7 0.003063 0.413476 0.013783 0.0045940.565084 8 0.000922 0.414810 0.014902 0.001383 0.567983 9 0.0003080.415193 0.015224 0.000461 0.568814 10 0.019417 0.388350 0.0226540.029126 0.540453 11 0.006601 0.396040 0.029703 0.009901 0.557756 120.001994 0.398804 0.032237 0.002991 0.563975 13 0.000666 0.3996000.032967 0.000999 0.565768 14 0.001069 0.391808 0.035619 0.0372220.534283 15 0.000357 0.392507 0.035682 0.036218 0.535236 16 0.0010690.356189 0.071238 0.072841 0.498664 17 0.000357 0.356824 0.0713650.071900 0.499554 18 0.000119 0.357037 0.071407 0.071586 0.499851 190.000119 0.285629 0.142815 0.142993 0.428444 20 0.000922 0.4148100.014902 0.001383 0.567983 21 0.000922 0.414810 0.014902 0.0013830.567983 22 0.000999 0.399401 0.032784 0.001498 0.565319 23 0.0009990.399401 0.032784 0.001498 0.565319 24 0.001089 0.381194 0.0539120.001634 0.562171 25 0.001089 0.381194 0.053912 0.001634 0.562171 260.001198 0.359353 0.079257 0.001797 0.558395 27 0.000881 0.4229700.005434 0.001322 0.569393 28 0.000881 0.422970 0.005434 0.0013220.569393 29 0.000894 0.420331 0.008496 0.001341 0.568937 30 0.0008940.420331 0.008496 0.001341 0.568937 Comparative example 1 0.0000000.392857 0.035714 0.035714 0.535714 2 0.000858 0.427652 0.0000000.001287 0.570203 3 0.004415 0.419426 0.005151 0.006623 0.564386 40.001478 0.421286 0.006652 0.002217 0.568367 5 0.000444 0.4219410.007180 0.000666 0.569768

TABLE 3 Composition of Mixture and Burning Temperature BurningComposition of mixture (wt %) temperature Si3N4 AlN Al203 Eu203 ° C.Embodiment 1 94.770 2.680 0.000 2.556 1900 2 97.460 1.300 0.000 1.2411900 3 95.200 1.030 0.000 3.771 1900 4 97.370 1.350 0.000 1.286 1900 598.150 1.460 0.000 0.389 1900 6 90.390 2.050 0.000 7.559 1900 7 94.6002.760 0.000 2.637 1900 8 96.170 3.030 0.000 0.804 1900 9 96.630 3.1100.000 0.269 1900 10 80.690 4.130 0.000 15.183 1900 11 88.620 5.830 0.0005.558 1900 12 91.770 6.500 0.000 1.727 1900 13 92.710 6.710 0.000 0.5821900 14 90.670 2.410 5.990 0.931 2000 15 91.240 2.420 6.030 0.312 200016 82.300 4.810 11.960 0.929 2000 17 82.810 4.840 12.040 0.312 2000 1882.980 4.850 12.060 0.104 2000 19 66.180 9.670 24.050 0.104 2000 2096.170 3.030 0.000 0.804 1900 21 96.170 3.030 0.000 0.804 2000 22 92.4806.650 0.000 0.870 1900 23 92.480 6.650 0.000 0.870 2000 24 88.130 10.9300.000 0.948 1900 25 88.130 10.930 0.000 0.948 2000 26 82.930 16.0300.000 1.040 1900 27 98.130 1.110 0.000 0.770 1900 28 98.130 1.110 0.0000.770 2000 29 97.490 1.730 0.000 0.780 1900 30 97.490 1.730 0.000 0.7802000 Comparative example 1 91.521 2.431 6.048 0.000 2000 2 99.251 0.0000.000 0.749 2000 3 95.200 1.030 0.000 3.771 1900 4 97.370 1.350 0.0001.286 1900 5 98.150 1.460 0.000 0.389 1900

Embodiments 2 to 24

In order to obtain a composition shown in Table 2 using the same rawmaterial powder as embodiment 1, the silicon nitride powder, thealuminum nitride powder and the europium oxide powder were weighedrespectively so as to be specified quantities, and were mixed for 2hours by a wet ball mill, using a pot made of silicon nitride sinter,balls made of silicon nitride sinter and n-hexane.

Dried mixture powder was obtained by removing n-hexane by means of arotary evaporator. A powder aggregate being excellent in flowability wasobtained by grinding the obtained mixture by means of an agate mortarand pestle and then passing the ground mixture through a sieve of 500μm.

This powder aggregate was put into a crucible made of boron nitride of20 mm in diameter and 20 mm in height by natural falling. Next, thecrucible was set on an electric furnace of a graphite resistance heatingtype. A burning process first made a burning atmosphere vacuum by meansof a diffusion pump, heated the crucible at a heating rate of 500°C./hour from room temperature to 800° C., introduced nitrogen of 99.999vol % in purity at 800° C. to make 1 MPa in pressure, heated thecrucible to 1900° C. or 2000° C. at a heating rate of 500° C./hour, andkept it at 1900° C. of 2000° C. for 2 hours.

The burnt materials obtained each contained a β-type Si₃N₄ or a β-typesialon of 50 wt % or more, and when a fluorescent spectrometry wasperformed, a fluorescent substance emitting a green light having a peakbetween 500 nm and 550 nm in wavelength by excitation of ultravioletrays to visible light as shown in Table 3 was obtained. Opticalcharacteristics of embodiments described above and comparative examplesto be disclosed in the following are collectively shown in Table 4.

TABLE 4 Fluorescent Characteristics of Embodiments and ComparativeExamples Burning Excitation Wavelength of Intensity, temperaturewavelength emitted light Arbitrary ° C. (nm) (nm) unit Embodiment 1 1900303 535 3948 2 1900 300 525 648 3 1900 298 524 95 4 1900 299 525 428 51900 299 525 731 6 1900 300 526 279 7 1900 300 527 1437 8 1900 300 5271861 9 1900 299 526 960 10 1900 299 527 292 11 1900 300 535 340 12 1900300 528 1553 13 1900 298 528 1783 14 2000 466 538 302 15 2000 305 535677 16 2000 467 544 1366 17 2000 308 543 1962 18 2000 306 542 1491 192000 405 546 1767 20 1900 301 534 3996 21 2000 307 535 6545 22 1900 303535 4391 23 2000 304 530 4826 24 1900 303 529 2996 25 2000 305 528 424826 1900 302 529 3544 27 1900 302 526 2812 28 2000 302 527 2079 29 1900302 528 5215 30 2000 301 528 4183 Comparative example 1 2000 2 2000 344592 285 3 1800 266 415 1271 4 1800 268 414 2024 5 1800 268 414 2318

Inorganic compound powder was made by a similar method to embodiments 2to 24, except compositions and burning temperatures shown in Tables 2,3.

Comparative example 1 has a composition close to embodiment 14 but doesnot contain Eu. An inorganic compound obtained by burning at 2000° C.for 2 hours was a β-sialon of z=0.5 but did not emit light at all evenby being excited by a light of 200 nm to 500 nm due to containing no Eu.

Comparative example 2 has a composition close to embodiment 20 but doesnot contain Al. An inorganic compound obtained by burning at 2000° C.for 2 hours was a β-type Si₃N₄ but did not emit a green light as shownin FIG. 6 since Eu remained in a grain boundary glass phase withoutbeing solid-dissolved into grains under this condition.

Comparative examples 3 to 5 have the same compositions as embodiments 16to 18 respectively, but are lower in burning temperature. An inorganiccompound obtained by burning at 1800° C. for 2 hours was a β-sialon ofz=1, but most of Eu remained as a grain boundary without beingsolid-dissolved into grains due to its low burning temperature andtherefore when being excited by ultraviolet rays it emitted a blue lightas shown in FIG. 7 and did not emit a green light.

Comparative Example 6

In order to synthesize a β-sialon of z=3 containing Eu in compositionSi₃Al_(2.97)Eu_(0.03)O_(8.03)N_(4.97), Si₃N₄ powder of 48.828 wt %, AlNpowder of 13.84 wt %, Al₂O₃ powder of 35.49 wt % and Eu₂O₃ powder of1.84 wt % were weighed, and mixed powder was made on the basis of thesame method and procedure as embodiment 1. This was burned at 1550° C.for 3 hours in a nitrogen atmosphere of 1 atm., being a burningcondition described in embodiment 23 of patent literature 5 using thesame burning furnace as embodiment 1.

When the spectrum of light emitted by excitation of the obtained powderwas measured, a violet light of 410 nm in wavelength was emitted asshown in FIG. 8 and was different from a green light emitted in thepresent invention.

Embodiment 31

Powder having the same composition as embodiment 1 was mixed for 2 hoursby a wet ball mill using a pot made of silicon nitride sinter, ballsmade of silicon nitride sinter and n-hexane. Dried mixture powder wasobtained by removing n-hexane by means of a rotary evaporator. A powderaggregate being excellent in flowability was obtained by grinding theobtained mixture by means of an agate mortar and pestle and then passingthe ground mixture through a sieve of 500 μm, and this powder aggregatewas put into a crucible made of boron nitride. Next, the crucible wasset on an electric furnace of a graphite resistance heating type. Aburning process first made a burning atmosphere vacuum by means adiffusion pump, heated the crucible at a heating rate of 500° C./hourfrom room temperature to 800° C., introduced nitrogen of 99.999 vol % inpurity at 800° C. to make 1 MPa in pressure, heated the crucible to2000° C. at a heating rate of 500° C./hour, kept it at 2000° C. for 8hours and then performed a heat treatment on it at 1700° C. for 24hours.

The burnt material obtained was slightly ground by means of an agatemortar made of silicon nitride and then its powder of about 5 g was putinto a beaker made of Teflon and had distilled water of 380 ml,hydrofluoric acid (made by WAKOJUNYAKU Co., Special Grade, 46% inconcentration) of 10 ml and sulfuric acid (made by WAKOJUNYAKU Co.,Special Grade, 95% in concentration) of 10 ml added to it, and wasstirred and mixed by a magnetic stirrer for 2 hours. After this, theacids were removed by cleaning with distilled water.

The spectra of light emitted by excitation before and after an acidtreatment are shown in FIGS. 9 and 10. A green fluorescent substance ofhigh luminance was obtained by this process A fluorescent substanceafter acid treatment has the intensity of emitted light exceeding agreen fluorescent substance of YAG:Ce on the market. When this powderwas observed by means of a scanning electron microscope, powder ofspherical grains each being about 3 μm in grain diameter and having anaspect ratio close to 1 was obtained. Further, when the powder wasobserved by means of a high-resolution transmission electron microscope,it has been confirmed that plane defects exist in a crystal and Euexists in the defective parts.

Next, an illuminator using a fluorescent substance made of nitride ofthe present invention is described.

FIG. 11 is a schematic structural diagram of a white LED as anilluminator.

This has a structure in which a blue LED 2 of 460 nm is used as a lightemitting device and the blue LED 2 is covered with a resin layer inwhich a fluorescent substance of embodiment 1 of the present inventionand a yellow fluorescent substance of Ca-α-sialon:Eu having compositionCa_(0.75)Eu_(0.25)Si_(8.625)Al_(3.375)O_(1.125)N_(14.875) are dispersed.

When an electric current is made to flow through conductive terminals,the LED 2 emits a light of 460 nm, and the yellow fluorescent substanceand a green fluorescent substance are excited by this light to emityellow and green lights respectively, and thus this illuminatorfunctions as an illuminator emitting a white light obtained by mixingthe LED light with the yellow and green lights. This illuminator washigh in color rendering ability due to having a green component incomparison with the case of singly using a yellow fluorescent substance.

An illuminator made by a different composition design from the abovecomposition is shown. This has a structure in which a blue LED of 460 nmis first used as a light emitting device and an ultraviolet LED iscovered with a resin layer in which a fluorescent substance ofembodiment 1 of the present invention and a red fluorescent substance(CaSiAlN₃:Eu) are dispersed. When an electric current was made to flowthrough conductive terminals, the LED emitted a light of 460 nm, and thered fluorescent substance and a green fluorescent substance were excitedby this light to emit red and green lights. This illuminator was able tofunction as an illuminator emitting a white light obtained by mixing ablue light emitted by the LED itself with the lights from thesefluorescent substances.

Further, an illuminator made by a different composition design from theabove composition is shown.

This has a structure in which an ultraviolet LED of 380 nm is first usedas a light emitting device and the ultraviolet LED is covered with aresin layer in which a fluorescent substance of embodiment 1 of thepresent invention, a blue fluorescent substance (BaMgAl₁₀O₁₇:Eu) and ared fluorescent substance (CaSiAlN₃:Eu) are dispersed. When an electriccurrent is made to flow through conductive terminals, the LED emits alight of 380 nm, and the red fluorescent substance, the greenfluorescent substance and the blue fluorescent substance are excited bythis light to emit red, green and blue lights, respectively. Thisilluminator was able to function as an illuminator emitting a whitelight obtained by mixing these lights.

Next, a design example of an image display device using a nitridefluorescent substance of the present invention is described.

FIG. 12 is a fundamental schematic diagram of a plasma display panel asan image display device. A green fluorescent substance of embodiment 1of the present invention, a red fluorescent substance (Y(PV)O₄:Eu) and ablue fluorescent substance (BaMgAl₁₀O₁₇:Eu) are respectively applied tothe inner faces of cells 11, 12 and 13.

When an electric current is made to flow through electrodes 14, 15, 16and 17, vacuum ultraviolet rays are generated by Xe-discharge in thecells and the fluorescent substances are excited by this and emitvisible lights of red, green and blue, and these lights are observedfrom the outside through a protective layer 20, a dielectric layer 19and a glass substrate 22; and thus this image display device has beenfound to be able to function as an image display.

INDUSTRIAL APPLICABILITY

A nitride fluorescent substance of the present invention is a nitridefluorescent substance to be used preferably in VFD, FED, PDP, CRT, whiteLED and the like, since it emits a green light differently from aconventional sialon fluorescent substance and oxy-nitride fluorescentsubstance, and further is less in reduction of luminance of thefluorescent substance in case of being exposed to an excitation source.After this, it can be expected that this fluorescent substance isgreatly utilized in material design for various display devices andcontributes to development of industry.

1. A fluorescent substance comprising a crystal of nitride oroxy-nitride having a β-type Si₃N₄ crystal structure having Eu⁺²solid-dissolved into it and emitting a fluorescent light having a peakwithin a range of 500 nm to 600 nm in wavelength by being irradiatedwith an excitation source, wherein said fluorescent substance furthercomprises another crystalline or amorphous compound different from saidnitride or oxy-nitride crystal and a quantity of said nitride oroxy-nitride crystal contained in said fluorescent substance is 50 wt %or more.
 2. A fluorescent substance according to claim 1, wherein saidanother crystalline or amorphous compound is an electrically conductiveinorganic compound.
 3. A fluorescent substance according to claim 2,wherein said electrically conductive inorganic compound is oxide,oxy-nitride, or nitride containing at least one element selected fromZn, Ga, In and Sn, or mixture thereof.
 4. A fluorescent substancemanufacturing method for manufacturing a fluorescent substance accordingto claim 1, comprising a process of burning a raw material mixturecontaining metal, oxide, carbonate, nitride, fluoride, chloride oroxy-nitride of Eu, silicon nitride and aluminum nitride at a temperatureof 1820° C. to 2200° C. in a nitrogen atmosphere.
 5. A fluorescentsubstance manufacturing method according to claim 4, wherein saidnitrogen atmosphere in said process of burning is a nitrogen atmospherewithin a pressure range of 0.1 MPa to 100 MPa.
 6. A fluorescentsubstance manufacturing method according to claim 4, further comprisinga process of filling a container with said raw material mixture in aform of powder or aggregate in a state of keeping said mixture at afilling factor of 40% or less in volume density before said process ofburning.
 7. A fluorescent substance manufacturing method according toclaim 6, wherein said container is made of boron nitride.
 8. Afluorescent substance manufacturing method according to claim 6, whereinsaid raw material mixture in the form of aggregate is 500 μm or less inaverage grain diameter.
 9. A fluorescent substance manufacturing methodaccording to claim 8, further comprising a process of making said rawmaterial mixture in the form of aggregate be 500 μm or less in averagegrain diameter by means of spray dryer, sieving or wind classification.10. A fluorescent substance manufacturing method according to claim 4,wherein said burning is made by using exclusively a normal pressuresintering method or a gas pressure burning method without using a hotpress.
 11. A fluorescent substance manufacturing method according toclaim 4, further comprising a process of grain-size-adjusting the burntfluorescent substance so as to be powder of 50 nm to 20 μm in averagegrain diameter by one or plural means selected from grinding,classification and acid treatment.
 12. A fluorescent substancemanufacturing method according to claim 11, further comprising a processof performing a heat treatment on the fluorescent substance after saidburning process or after said grain size adjusting process at atemperature not lower than 1000° C. and lower than a burning temperaturein said process of burning.
 13. A fluorescent substance manufacturingmethod for manufacturing a fluorescent substance comprising a crystal ofnitride or oxy-nitride having a β-type Si₃N₄ crystal structure havingEu⁺² solid-dissolved into it and emitting a fluorescent light having apeak within a range of 500 nm to 600 nm in wavelength by beingirradiated with an excitation source, said method comprising a processof burning a raw material mixture containing metal, oxide, carbonate,nitride, fluoride, chloride or oxy-nitride of Eu, silicon nitride andaluminum nitride at a temperature of 1820° C. to 2200° C. in a nitrogenatmosphere, wherein said raw material mixture contains an inorganiccompound forming a liquid phase at a temperature not higher than theburning temperature in said process of burning.
 14. A fluorescentsubstance manufacturing method according to claim 13, wherein saidinorganic compound forming the liquid phase at a temperature not higherthan said burning temperature comprises at least one of fluoride,chloride, iodide, bromide and phosphate of at least one element selectedfrom Li, Na, K, Mg, Ca, Sr and Ba.
 15. A fluorescent substancemanufacturing method according to claim 14, wherein said inorganiccompound forming the liquid phase at a temperature not higher than saidburning temperature is calcium fluoride.
 16. A fluorescent substancemanufacturing method according to claim 13, wherein said raw materialmixture contains the inorganic compound forming the liquid phase at atemperature not higher than said burning, temperature at the ratio of0.1 to 10 in weight of said inorganic compound to 100 in weight of saidraw material mixture.
 17. A fluorescent substance manufacturing methodaccording to claim 13, further comprising a process of cleaning saidburnt mixture with a solvent so as to reduce quantity of said inorganiccompound forming the liquid phase at a temperature not higher than saidburning temperature after said burning process.
 18. An image displaydevice comprising an excitation source and a fluorescent substance,wherein said fluorescent substance comprises the fluorescent substanceaccording to claim
 1. 19. An image display device according to claim 18,comprising at least one of a fluorescent display tube, a field emissiondisplay, a plasma display panel and a cathode ray tube.
 20. An imagedisplay device comprising an excitation source and a fluorescentsubstance, wherein said fluorescent substance comprises the fluorescentsubstance according to claim
 1. 21. An image display device according toclaim 20, comprising at least one of a fluorescent display tube, a fieldemission display, a plasma display panel and a cathode ray tube.